ML23305A167

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November 14, 2023 Public Meeting Presentation
ML23305A167
Person / Time
Issue date: 11/01/2023
From: Marshall M
Division of Operating Reactor Licensing
To:
Office of Nuclear Reactor Regulation
References
EPID L-2023-NNR-0007
Download: ML23305A167 (1)
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Text

Public Meeting November 14, 2023 SRM-SECY-22-0076 Implementation:

Branch Technical Position 7-19, Draft Revision 9

Meeting Purpose This is an information meeting to provide external stakeholders an opportunity to ask the NRC staff questions about the draft revision to BTP 7-19.

  • The NRC staff will not be collecting comments on the draft BTP as part of this meeting.
  • To provide comments on the draft BTP revision:
  • Follow instructions for providing comments 2

Opening Remarks

Presentation Outline

  • SRM-SECY-22-0076 Direction and Staff Proposed Response
  • Substantive Changes to BTP 7-19
  • Next Steps
  • Question and Answer Session
  • Closing Remarks 4

SRM-SECY-22-0076

  • The Commission approved the staffs recommendation to expand the existing policy for digital I&C CCFs to allow the use of risk-informed approaches to demonstrate the appropriate level of defense-in-depth, subject to the edits provided
  • The Commission directed the staff to clarify, in the implementing guidance, that the new policy is independent of the licensing pathway selected by the reactor licensees and applicants
  • The Commission directed the staff to complete the final implementing guidance within a year from the date of the SRM (May 24, 2024) 5

Substantive Changes to BTP 7-19

  • Revised Section B.1.1 to reflect the updated four points in SRM-SECY-22-0076
  • Revised Section B.1.2 for clarification of critical safety functions
  • Revised Section B.3.1.3 for evaluation of alternative approaches
  • Added Section B.3.4 for evaluation of risk-informed D3 assessment
  • Revised Section B.4 for evaluation of different approaches for meeting Point 4
  • Added four flowcharts to facilitate the review 6

Staff Proposed Response to Meet the SRM Staff drafted Revision 9 to SRP BTP 7-19

  • Allows the staff to review risk-informed applications
  • May result in use of design techniques other than diversity
  • Focused the revisions on implementing the expanded policy 7

Updated Four Points of the Policy (Section B.1.1)

  • Replaced the four SRM-SECY-93-087 points with the SRM-SECY-22-0076 points
  • Updated the explanation of the four points to reflect the language in the SRM-SECY-22-0076 points
  • Identified the applicable BTP sections for the evaluation of an application against these four points 8

Critical Safety Functions (Section B.1.2)

  • Clarified that critical safety functions are those most important safety functions to be accomplished or maintained to prevent a direct and immediate threat to the health and safety of the public
  • Clarified that the critical safety functions identified in SECY-93-087 are examples representative of operating light water reactors
  • Clarified that other types of reactors may have different critical safety functions based on the reactor design safety analysis
  • The identification of such functions may be risk-informed 9

Alternatives to Diversity (Section B.3.1.3)

Two Pathways

  • Previous endorsement (e.g., RG) or approval (e.g., precedent or Topical Report)
  • Ensure it is applicable
  • Ensure it is followed
  • Justify any deviations
  • A new approach proposed as part of an application
  • Use the acceptance criteria in BTP 7-19
  • Review description of vulnerability being addressed
  • Review description of alternative approach and justification 10

Risk-Informed D3 Assessment Process 11 Identify each postulated CCF Address the CCF using a risk-informed approach Model the CCF in the PRA (Section B.3.4.2)

Determine the risk significance of the CCF (Section B.3.4.3)

Determine appropriate means to address the CCF (Section B.3.4.4)

Determine consistency with NRC policy and guidance on RIDM (Section B.3.4.1)

Address the CCF deterministically Justify alternative approaches

Risk-Informed D3 Assessment (Section B.3.4.1)

Determine Consistency with NRC Policy and Guidance on RIDM

  • Review applications that use risk-informed approaches for consistency with established NRC policy and guidance on RIDM
  • Current staff review guidance includes:
  • SRP Chapter 19 provides review guidance for addressing the principles of risk-informed decision-making, including defense in depth 12

Risk-Informed D3 Assessment (Section B.3.4.2)

Model the CCF in the PRA

  • Determine if the base PRA meets PRA acceptability guidance identified in the application
  • Evaluate how the CCF is modeled in the PRA and the justification that the modeling adequately captures the impact of the CCF on the plant
  • Options for modeling the CCF in the PRA include:
  • Detailed modeling of the DI&C system
  • Use of surrogate events
  • Follow identified PRA acceptability guidance to determine if CCF modeling is a PRA upgrade or maintenance 13

Risk-Informed D3 Assessment (Section B.3.4.3)

Determine the Risk Significance of the CCF

  • The risk significance of a CCF can be determined using a bounding sensitivity analysis or a conservative sensitivity analysis
  • A bounding sensitivity analysis:
  • Assumes the CCF occurs
  • Provides a description of the baseline risk
  • A conservative sensitivity analysis:
  • Provides a technical basis for a conservative probability (less than 1) of the CCF, demonstrating that all principles of RIDM, especially defense in depth and safety margins, are addressed
  • Addresses the impact of this assumption on PRA uncertainty 14

Risk-Informed D3 Assessment (Section B.3.4.3)

Determine the Risk Significance of the CCF

  • The quantification accounts for any dependencies introduced by the CCF, including the ability for operators to perform manual actions
  • A CCF is not risk significant if the following criteria are met for the sensitivity analysis:
  • The increase in CDF is less than 1 x 10-6 per year
  • The increase in LERF is less than 1 x 10-7 per year 15

Risk-Informed D3 Assessment (Section B.3.4.4) 16

Risk-Informed D3 Assessment (Section B.3.4.4)

  • If a CCF is not risk significant, standard design and verification and validation processes are sufficient to address the CCF
  • If a CCF is risk significant, the following apply, with a level of technical justification commensurate with the risk significance of the CCF:
  • The application identifies the CCF vulnerabilities or causes
  • The application provides a description of how it addresses the CCF vulnerabilities or causes (including any conditions or limitations)
  • The application provides a technical basis explaining how it addresses the identified CCF vulnerabilities or causes and prevents or mitigates their effects 17

Approaches for Meeting Point 4 (Section B.4) 18

  • Section B.4 provides six acceptance criteria for independent and diverse main control room displays and controls for manual actuation of critical safety functions
  • Applications that propose a different approach (i.e., one that does not meet all the acceptance criteria in B.4) provide appropriate justification

Flowcharts to Facilitate the Use of the BTP

  • Added four flowcharts at the end of the BTP:
  • Figure 7-19-1. Point 1 - Need for a Detailed D3 Assessment
  • Figure 7-19-2. Point 2 - Detailed Assessment
  • Figure 7-19-3. Point 3 - Addressing, Mitigating or Accepting the Consequences of Each CCF
  • Figure 7-19-4. Point 4 - Independent and Diverse Displays and Manual Controls
  • The flowcharts provide a visual aid to the reviewers when reviewing an application against the four points
  • Identify the conceptual steps for performing the review
  • Identify the applicable BTP sections 19

Next Steps

  • The public comment period ends on November 24, 2023
  • The staff is planning to issue the final BTP 7-19, Rev. 9 in May 2024 20

This is an information meeting to provide external stakeholders an opportunity to ask the NRC staff questions about the draft revision to BTP 7-19.

  • The NRC staff will not be collecting comments on the draft BTP as part of this meeting.
  • To provide comments on the draft BTP revision:
  • Follow instructions for providing comments 21 Reminder: Meeting Purpose

Question and Answer Session

Closing Remarks

Acronyms ACRS Advisory Committee on Reactor Safeguards BTP Branch Technical Position CCF Common Cause Failure CDF Core Damage Frequency D3 Defense-in-Depth and Diversity DAS Diverse Actuation System DI&C Digital Instrumentation and Control DRG Design Review Guide ESFAS Engineered Safety Features Actuation System GDC General Design Criteria I&C Instrumentation and Control ISG Interim Staff Guidance LERF Large Early Release Frequency LMP Licensing Modernization Project LWR Light-Water Reactor NEI Nuclear Energy Institute NRC Nuclear Regulatory Commission PRA Probabilistic Risk Assessment RG Regulatory Guide RIDM Risk-Informed Decision-Making RPS Reactor Protection System SECY Commission Paper SRM Staff Requirements Memorandum SRP Standard Review Plan

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